David Cameron today announced 10,000 soldiers will be ready to surge onto Britain’s streets in the event of a Paris-style terror attack.

The Prime Minister delivered a statement on the Government's security and defence review to MPs, having this morning visited the Bataclan theatre in Paris where 89 were slaughtered by ISIS terrorists just over a week ago.

Overall, 129 people were killed in a series of shootings and suicide bombings int he French capital.

Mr Cameron told the House of Commons should a similar attack take place in the UK, a new operation had been drawn up to allow thousands of troops to protect Britons.

He said: "I can tell the House today we have put in place a significant new contingency plan to deal with major terrorist attacks.

"Under this new operation up to 10,00 military personnel will be available to support the police in dealing with the type of shocking terrorist attacks we have seen in Paris."

The Prime Minister also confirmed the Government would "increase our investment in counter-terrorism police" as well as "more than double our spreading on aviation security around the world".

Describing ISIS as "not some remote problem thousands of miles away", Mr Cameron announced he will set out the case for Britain to bomb the terrorist group in Syria, as well as in Iraq, in the House of Commons.

Mr Cameron also announced plans for new patrol aircraft to hunt down Russian submarines in British waters; 1,900 new British spies; two new 'strike brigades' of 5,000 crack troops each to respond to conflicts across the world at short notice; £2bn for special forces including the SAS; new cyber security funding; and new drones to spy on enemy states and terror groups from the edge of space.

But, the Government was also today forced to admit replacing the Royal Navy's ageing fleet of submarines that carry Britain's Trident nuclear deterrent could cost up to £40bn.

The Ministry of Defence now estimates that buying four new submarines will cost £31 billion over 20 years, compared to a previous estimate of £25 billion.

And a further £10bn "contingency" has been set aside to meet additional unexpected cost increases.